Communication devices such as wireless devices are also known as e.g. User Equipments (UE), mobile terminals, wireless terminals and/or mobile stations. Wireless devices are enabled to communicate wirelessly in a communications network or wireless communication system, sometimes also referred to as a radio system or networks. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the communications network.
Wireless devices may further be referred to as mobile telephones, cellular telephones, laptops, or surf plates with wireless capability, just to mention some further examples. The terminals in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
The communications network may cover a geographical area which may be divided into cell areas, wherein each cell area may be served by an access node such as a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE controlled by the radio base station.
Communications such as transmissions in radio communication systems may be often organized in terms of frames, or sometimes subframes, e.g. in LTE, where each frame is a group of communication resources, e.g., radio time and frequency resources, that may comprise both, a control field and a payload data field, or multiple fields of the respective types. A field may be understood herein to refer to a set of time and frequency resources, also referred to herein as time-frequency resources. The time-frequency resources corresponding to a field may be contiguous in the time and frequency dimensions. The control field may, e.g., comprise information about how the data part of the frame is encoded and modulated. The control field may also be used for receiving feedback information in the reverse link direction, i.e., from the receiver of the data, e.g., for receiving ACKnowledgement/Negative ACKnowledgement (ACK/NACK) or channel state information reports.
Fields may be in most transmission systems further divided into smaller units, e.g., in Orthogonal Frequency-Division Multiplexing (OFDM) systems, the fields may be further divided into one or more OFDM symbols. Something similar holds for many other types of systems than OFDM, e.g., for many systems based on multi-carrier transmission or pre-coded multi-carrier transmission, such as Filter-Bank Multi-Carrier (FBMC), Discrete Fourier Transform (DFT)-spread OFDM, etc. As a general term, such smaller units may be referred to herein as symbols. Some fields may consist of only a single symbol.
LTE may use OFDM in the DL and DFT-spread OFDM in the UL. The basic LTE DL physical resource may thus be seen as a time-frequency grid as illustrated in FIG. 1, where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval.
In the time domain, LTE DL transmissions may be organized into radio frames of 10 milliseconds (ms), each radio frame consisting of ten equally-sized subframes of length Tsubframe=1 ms. FIG. 2 is a schematic illustration of the LTE time-domain structure.
The resource allocation in LTE may be typically described in terms of resource blocks, where a resource block corresponds to one slot, 0.5 ms, in the time domain and 12 contiguous subcarriers in the frequency domain. A pair of two adjacent resource blocks in time direction, 1.0 ms, is known as a resource block pair. Resource blocks may be numbered in the frequency domain, starting with 0 from one end of the system bandwidth.
Carrier Aggregation
The use of LTE Carrier Aggregation (CA), introduced in Rel-10 and enhanced in Rel-11, may offer means to increase the peak data rates, system capacity and user experience by aggregating radio resources from multiple carriers that may reside in the same band or different bands and, for the case of inter-band Time-Division Duplex (TDD) CA, the carriers may be configured with different UL/DL configurations. In Rel-12, CA between TDD and Frequency-Division Duplex (FDD) serving cells was introduced to support UE connecting to them simultaneously. Up to this release, the maximum number of carriers which are supported is 5.
In Rel-13, Licensed-Assisted Access (LAA) has attracted a lot of interest in extending the LTE CA feature towards capturing the spectrum opportunities of unlicensed spectrum in the 5 GHz band. WLAN operating in the 5 GHz band nowadays may already support 80 Mega Hertz (MHz) in the field, and 160 MHz is to follow in Wave 2 deployment of IEEE 802.11ac. There are also other frequency bands, such as 3.5 Giga Hertz (GHz), where aggregation of more than one carrier on the same band may be possible, in addition to the bands already widely in use for LTE. Enabling the utilization of at least similar bandwidths for LTE in combination with LAA, as IEEE 802.11ac Wave 2, may support calls for extending the carrier aggregation framework to support more than 5 carriers. The extension of the CA framework beyond 5 carriers was approved to be one work item for LTE Rel-13. The objective is to support up to 32 carriers in both UL and DL.
A UE may typically report feedback to the serving network node on the quality of the carrier that carries information that may be exchanged between the serving network node and the UE. This may be done so the network node may for example adjust some transmission parameters, to improve the quality or efficiency of the communication between the network node and the UE. Compared to single-carrier operation, a UE operating with CA may have to report feedback for more than one DL component carrier. However, a UE may not need to support DL and UL CA simultaneously. For instance, the first release of CA capable UEs in the market may only support DL CA, but not UL CA. This is also the underlying assumption in the 3GPP RAN4 standardization. Hence, support of DL CA may lead to feedback for multiple DL carriers being carried in one single UL carrier. The capacity of UL control channel for single carrier operation cannot meet the new capacity requirements. Therefore, to address this problem, an enhanced UL control channel, i.e. Physical Uplink Control CHannel (PUCCH) format 3, was introduced in the first release of CA. Such an UL control channel may carry the feedback information from the UE, and is further described in the next section. However, in order to support more component carriers in Rel-13, the UL control channel capacity becomes a limitation. More specifically, Rel-10 PUCCH format 3 supports up to 10-bit Hybrid Automatic Repeat reQuest ACK (HARQ-ACK) for FDD and 20-bit for TDD, but a UE configured with 32 DL Component Carriers (CCs) may need up to 64 bits HARQ-ACK for FDD, and even more for TDD. Generally, one HARQ-ACK bit may be needed for one DL transport block. In LTE, at most two transport blocks may be supported for allocation to a single UE during a subframe in one serving cell, which corresponds to 2 HARQ-ACK bits.
PUCCH Format 3
To support the transmission of DL and UL transport channels, there may be a need for UL L1/L2 control signaling. UL L1/L2 control signaling may carry control information and may comprise: HARQ acknowledgements for acknowledging whether the received Physical Downlink Shared CHannel (PDSCH) transport blocks have been correctly received or not, or whether they have been missed, channel-state reports related to the DL channel conditions, such as Channel State Information (CSI), used to assist DL scheduling, and scheduling requests, indicating that a terminal needs UL resources for UL-SCH transmissions.
In LTE, three PUCCH formats with different sizes may be defined which may support the transmission of the above-described UL L1/L2 control signaling for different purposes.
In LTE PUCCH format 1/1a/1b and PUCCH format 2/2a/2b may be supported for Scheduling Request (SR), HARQ-ACK and periodic Channel State Information (CSI) reporting. A PUCCH resource may be understood as a physical resource unit which may be used to convey L1/L2 control signaling. Physically, a PUCCH resource may correspond to one or several physical resource blocks together with some other transmit parameters such as cyclic shift, orthogonal cover code, spreading code, etc . . . . The PUCCH resource may be represented by a single scalar index, that is, a number, from which parameters, e.g., transmission parameters, such as the phase rotation and/or the orthogonal cover sequence, may be derived, based on PUCCH format. The use of a phase rotation of a cell-specific sequence together with orthogonal sequences may provide orthogonality between different terminals in the same cell transmitting PUCCH on the same set of resource blocks. In LTE Rel-10, PUCCH format 3 was introduced for carrier aggregation and TDD, when there are multiple DL transmissions, either on multiple carriers or multiple DL subframes, but single UL, either single carrier or single UL subframe, for HARQ-ACK, SR and CSI feedback.
Similarly to PUCCH format 1/1a/1b and PUCCH format 2/2a/2b, the PUCCH format 3 resource may be also represented by a single scalar index, e.g., an integer ranging from 0 to 549, from which the orthogonal cover sequence and the resource-block number may be derived. Physically, a PUCCH format 3 resource may correspond to one physical resource block together with some other transmit parameters such as cyclic shift, orthogonal cover code, spreading code, etc . . . . A length-5 orthogonal sequence may be applied for PUCCH format 3 to support code multiplexing within one resource-block pair, according to 3GPP TS 36.211, and a length-4 orthogonal cover may be applied for a shorted PUCCH, wherein one OFDM symbol is punctured for SRS transmission in the second slot. If the PUCCH format 3 resource is denoted as nPUCCH(3), the resource block number, that is an identifier for each resource block, of the PUCCH format 3 resource m may be determined by the following:m=└nPUCCH(3)/NSF,0PUCCH┘
The orthogonal cover sequence applied for the two slots corresponding to the resource-block pair may be derived by the following:
            n              oc        ,        0              =                  n        PUCCH                  (          3          )                    ⁢      mod      ⁢                          ⁢              N                  SF          ,          1                PUCCH                        n              oc        ,        1              =          {                                                                  (                                  3                  ⁢                                                                          ⁢                                      n                                          oc                      ,                      0                                                                      )                            ⁢              mod              ⁢                                                          ⁢                              N                                  SF                  ,                  1                                PUCCH                                                                                        if                ⁢                                                                  ⁢                                  N                                      SF                    ,                    1                                    PUCCH                                            =              5                                                                                          n                                  oc                  ,                  0                                            ⁢              mod              ⁢                                                          ⁢                              N                                  SF                  ,                  1                                PUCCH                                                          otherwise                              
Where NSF,0PUCCH and NSF,1PUCCH are the length of the orthogonal cover sequence for the two slots respectively.
The PUCCH format 3 resource may be determined according to higher layer configuration and a dynamic indication from the downlink assignment. In detail, the Transmitter Power Control (TPC) field in the Downlink Control Information (DCI) format of the corresponding Physical Downlink Control CHannel (PDCCH)/Enhanced PDCCH (EPDCCH) may be used by a network node such as an eNB to determine the PUCCH resource values from one of four resource values configured by higher layers, with the mapping defined in Table 1, according to 3GPP TS 36.213. According to Table 1, four candidate resources may be configured at a network node by the higher layers. For each PUCCH transmission, one resource may be selected from the four candidate resources and indicated to a wireless devices via the TPC field. Each of these resource values is the scalar index. For FDD, the TPC field may correspond to the PDCCH/EPDCCH for the scheduled secondary serving cells. For TDD, the TPC field may correspond to the PDCCH/EPDCCH for the primary cell with Downlink Assignment Index (DAI) value in the PDCCH/EPDCCH larger than ‘1’. For a given UE, several PDCCH assignments may be sent to the UE in order to schedule PDSCH transmissions on more than one serving cell, with e.g. one-to-one mapping between PDCCH assignment and PDSCH transmission. Based on PUCCH format 3 capacity and the maximum configurable DL carriers number, only one PUCCH format 3 may be needed to be configured in Rel-12. According to current specification requirements, a UE may assume that the same PUCCH resource values are transmitted in each DCI format of the corresponding PDCCH/EPDCCH assignments that may be used to determine the PUCCH for this UE in the subframe. With the duplicate transmission of the same PUCCH resource values, the UE avoid the PUCCH resource ambiguity in case some of DCI are missing.
TABLE 1PUCCH Resource Value for HARQ-ACK Resource for PUCCHValue of ‘TPC commandfor PUCCH’ or‘HARQ-ACK resource offset’nPUCCH(3, {tilde over (p)})‘00’The 1st PUCCH resource valueconfigured by the higher layers‘01’The 2nd PUCCH resource valueconfigured by the higher layers‘10’The 3rd PUCCH resource valueconfigured by the higher layers‘11’The 4th PUCCH resource valueconfigured by the higher layers
According to the foregoing, existing PUCCH formats do not support the current demands for CA since their capacity is not sufficient to enable UEs to send the necessary amount of bits of information in the UL, e.g., for HARQ signaling which may be associated with the increase in the number of DL carriers. As indicated above in regards to carrier aggregation, the 3GPP Release 13 aims to support up to 32 CCs in both UL and DL. For this purpose, the capacity of the PUCCH, which is the channel that may carry the UL feedback information from the UE, may become a limitation. This may be a problem, especially for UEs not supporting DL and UL CA simultaneously, where the UE may have to transmit UL control signaling information corresponding to a large number of DL component carriers on a single UL carrier. For UEs only supporting DL CA, the UL control information may only be transmitted on the primary UL carrier, as it may be done in Rel-10. As an example, if 32 DL CCs are configured for a given UE and two transport blocks are scheduled on each CC, then the UE may need to feedback 64 bits HARQ-ACK in one subframe, which exceeds the maximum capacity of PUCCH format 3, 20 bits for TDD and 10 bits for FDD. If e.g., PUCCH format 3, is still used, when the number of DL component carriers exceed a certain number of carriers, e.g., 10, or 32 DL carriers, a UE has to drop or abandon some UL control information due to the capacity limitation. With the loss of this information, the network node may need to retransmit PDSCH or has no way to adjust the transmission parameters to adapt to the channel condition, thus leading to deterioration of the DL spectrum efficiency.